1. Field of the Invention
The present invention relates to a frontend circuit.
2. Description of the Related Art
It has already been decided that a transition will be made from the current analog TV broadcast to ground-wave digital TV broadcast. In view of this, not only ICs for reception of digital TV broadcasts but also DSPs (digital signal processors) capable of processing a received digital signal have been developed.
However, in the transition performance from the analog TV broadcast to the digital TV broadcast, analog TV broadcasts and digital TV broadcasts will exist in a mixed manner.
In such a situation, to receive those two kinds of TV broadcasts, both of a frontend circuit (tuner circuit) for receiving an analog TV broadcast and outputting a video signal and an audio signal and a frontend circuit for receiving a digital TV broadcast and outputting a video signal and an audio signal will be necessary.
An object of the present invention is therefore to make it possible to receive both of analog TV broadcasts and digital TV broadcasts by means of a common, single frontend circuit.
An exemplary frontend circuit according to the invention comprises a first band-pass filter for separating and taking out an audio intermediate frequency signal from an input intermediate frequency signal; a first A/D converter circuit for A/D converting the audio intermediate frequency signal taken out by the first band-pass filter into a digital audio intermediate frequency signal; a first DSP for performing audio detection on the digital audio intermediate frequency signal that is output from the first A/D converter circuit, and for forming a first AGC (automatic gain control) signal based on the digital audio intermediate frequency signal; a variable gain amplifier provided on a signal line between the first band-pass filter and the first A/D converter circuit, for performing AGC on the audio intermediate frequency signal using the first AGC signal; a second band-pass filter for separating and taking out a video intermediate frequency signal from the input intermediate frequency signal; a second A/D converter circuit for A/D converting the video intermediate frequency signal taken out by the second band-pass filter into a digital video intermediate frequency signal; and a second DSP for performing video detection on the digital video intermediate frequency signal that is output from the second A/D converter circuit, and for forming a second AGC signal based on the digital video intermediate frequency signal, wherein control is so made that AGC is performed on the input intermediate frequency signal by using the second AGC signal.
With the above configuration, whether an analog TV broadcast or a digital TV broadcast is received, both of an audio signal and a video signal are demodulated by digital processing.